The Met Office has downgraded its forecast for global warming to suggest that by 2017 temperatures will have remained about the same for two decades. “We are investigating why the temperature rise at the surface has slowed in recent years.”

A new scientific model has revised previous figures for the next five years downwards by around a fifth.

The forecast compares how much higher average world temperatures are likely to be than the “long-term average” from 1971-2000.

It had been thought that this would be 0.54C during the period 2012 -2016 but new data puts the figure for the 2013-2017 period at 0.43C.This figure is little higher than the 0.40C recorded in 1998, the warmest year in the Met Office Hadley Centre’s 160-year record – suggesting global warming will have stalled in the intervening two-decade period.

However, it is thought that factors such as ocean current patterns may be behind the slowdown and scientists say the “variability” in climate change does not alter the long-term trend of rising temperatures.

The new annual forecast, published on December 24, is the first to make use of the Met Office’s latest climate model, HadGEM3, which it said “includes a comprehensive set of improvements based on the latest scientific understanding”.

It suggests that global average temperature will remain between 0.28C and 0.59C above the long-term average “with values most likely to be about 0.43C higher than average”.

The Met Office said: “This is an extremely challenging area of research not least because long-term comprehensive observations of the ocean do not exist to help us understand how the global oceans behave over decadal and longer timescales.

“As with all areas of science, our knowledge is continually increasing and it is therefore not surprising that our models and predictive skill will continue to improve.

“The fact that the new model predicts less warming, globally, for the coming five years does not necessarily tell us anything about long-term predictions of climate change for the coming century.”

Figures from last November, showing that 2012 would be cooler than average for the past decade, had already indicated that global warming was slowing down.

Dr Peter Stott, Head of Climate Monitoring and Attribution at the Met Office, said at the time that the past decade had been the warmest on record.

But he pointed out that warming has slowed down since 2000, in comparison to the rapid warming of the world since the 1970s.

“Although the first decade of the 21st century was the warmest on record, warming has not been as rapid since 2000 as over the longer period since the 1970s,” he said. “This variability in global temperatures is not unusual, with several periods lasting a decade or more with little or no warming since the instrumental record began.

“We are investigating why the temperature rise at the surface has slowed in recent years, including how ocean heat content changes and the effects of aerosols from atmospheric pollution may have influenced global climate.”

Dr Stott warned that global warming could speed up again at any time, and insisted that the general pattern of warming was not in doubt.